Embodiments of the present invention generally relate to an environmental control system for an aircraft and, more particularly, to cooling a ram air fan motor for the environmental control system of an aircraft.
An environmental control system (ECS) aboard an aircraft provides conditioned air having a desirable temperature, pressure, and humidity for aircraft passenger comfort and safety to an aircraft cabin. When the aircraft is at or near ground level, the ambient air temperature and/or humidity is often sufficiently high that the air must be cooled as part of the conditioning process before being delivered to the aircraft cabin. At flight altitude, however, ambient air is often far cooler than desired, but at such a low pressure that it must be compressed to an acceptable pressure as part of the conditioning process. Compressing ambient air at flight altitude heats the resulting pressurized air sufficiently that it must be cooled, even if the ambient air temperature is very low. Thus, under most conditions, heat must be removed from air by the ECS before the air is delivered to the aircraft cabin. As heat is removed from the air, it is dissipated by the ECS into a separate stream of air that may come from a ram air system and that is referred to as ram air herein. The ram air flows into the ECS, across heat exchangers in the ECS, and out of the aircraft, carrying the excess heat with it. Under conditions where the aircraft is moving fast enough, the pressure of the ram as it enters the aircraft is sufficient to move enough air through the ECS and over the heat exchangers to remove the excess heat.
While ram air works well under normal flight conditions, at lower flight speeds, or when the aircraft is on the ground, the ram air pressure is too low to provide enough air flow across the heat exchangers for sufficient heat removal from the ECS. Under these conditions, a fan within the ECS is employed to provide the necessary airflow across the ECS heat exchangers. The fan is driven by an electric motor which, in turn, must also be cooled by air flowing across it. Cooling flow is drawn from a heat exchanger inlet and across the electric motor to the ram fan inlet.